I am new to keeping Betta, and my sister and I both got a Betta. We have 2 gallon tanks, and about an how ago I put the tanks next to each other and the fish were staring at each other and started to flair. Is this taunting each other since they probably want to fight? Thank you!

Are they both male? Betta fish are quite aggressive one with the other. Their other name is Siamese fighting fish. If they meet upclose they will fight and there can be fatal results (most of the time). Even males and females fight even before and after breeding. So to answer your q, yes they taunt each other, or more accurately they try to intermediate one another.

I suggest you keep their containers a small distance one from the other as they wont flare at each other all the time and wont get stressed.

You can keep female betta fish in a large aquarium but they need specific numbers, lots of plants and hiding places. They will try to form a hierarchy of sorts by fighting one another for a time, hopefully without casualties and then stop and coexist.

They quite taunt one another and are in a mood for a catfight so to speak. Like that (seperated) they will never sort their order differences on who will be the dominant one though and will continue to flair at one another and get stressed. You can either put them in a large tank together (I am not sure if 2 is a good number though, regardless I would recommend a 10g) with lots of hiding places and well planted or keep their containers at a fair distance to avoid stress issues. You can tell from the bars/stripes forming on their bodies (cant remember which is, vertical or horizontal).

It's good exercise to flare them at each other regularly. Breeders do this to keep the fish in shape.

It may sound a bit rude but its not my intention so please pardon me beforehand if it sounds like that but: Why? Do they need to keep their abs in shape? Swimming isnt enough? Hahahaha, lets get them to the betta gym :P

Stress from feeling threatened will be more harmful to their health than not exercising their abs :)